Field of the Invention
The present invention relates to a semiconductor encapsulation resin composition; and a semiconductor device comprising a cured product of such composition.
Background Art
In recent years, as a countermeasure(s) against global warming, there have been promoted global-scale environmental actions such as energy source conversions from fossil fuels. For this reason, in the automotive field, the number of hybrid vehicles and electric vehicles manufactured has increased. Further, in emerging countries such as China and India, there have been seen more types of home electronics equipped with an inverter motor as an energy saving measure.
In the case of hybrid and/or electric vehicles and invertor motors, a power semiconductor is critical for converting alternate current to direct current or vice versa, and for performing voltage transformation. However, silicon (Si) which has been used as a semiconductor for many years is approaching its performance limitation. For example, it has become difficult to expect a drastic performance improvement as is the case where lowering of the resistance of a power MOSFET is attempted to reduce power loss at the time of power conversion. Here, much attention has been drawn to next-generation power semiconductors employing wide band-gap semiconductors such as silicon carbide (SiC), gallium nitride (GaN) and diamond. Particularly, developments are being made in the production of a low-loss power MOSFET using SiC.
As wide band-gap semiconductors, SiC and GaN have a superior property that their band gaps are about 3 times wider than that of Si, and their breakdown field strengths are 10 or more times higher than that of Si. Also, these wide band-gap semiconductors have features such as a high-temperature operation (reportedly operable at 650° C. in the case of SiC), a high thermal conductivity (same level as Cu in the case of SiC) and a high saturated electron drift velocity. Due to these features, the on resistance of a power semiconductor can be lowered by employing SiC and GaN, such that the power loss in a power converter circuit can be drastically reduced.
A power semiconductor is usually protected through transfer molding using an epoxy resin and/or through potting encapsulation using a silicone gel. In these days, from the perspective of reduction in size and weight, transfer molding using an epoxy resin has almost become a mainstream encapsulation method. However, although an epoxy resin is a well-balanced heat curable resin superior in adhesion to a base material and in-mechanical strength, a heat decomposition at crosslinked points will progress at a temperature higher than 200° C. For this reason, there has been a concern that an epoxy resin may not be able to serve as an encapsulation material under such a high-temperature operation environment as it is expected of SiC and GaN (see ENGINEERING MATERIALS November issue of 2011 (vol. 59 No. 11) p. 58 to 63).
Here, as a material superior in heat resistance, there has been considered a heat curable resin composition containing a cyanate resin(s). For example, Japanese Examined Patent Publication No. H6-15603 discloses that a stable heat resistance can be achieved by allowing an oxazole ring(s) to be formed in a cured product of a phenol novolac resin. Such oxazole ring(s) are formed by a reaction of a multivalent cyanate ester and an epoxy resin. Further, Japanese Examined Patent Publication No. H6-15603 discloses that a cured product superior in heat and water resistances can be obtained when the hydroxyl equivalent of a phenol novolac resin is 0.4 to 1.0, and the cyanato group equivalent of a multivalent cyanate ester is 0.1 to 0.6, with respect to 1 epoxy equivalent of an epoxy resin. Furthermore, JP-A-2013-53218 describes that a heat curable resin composition having a particular structure and containing a cyanate ester compound, a phenolic compound and an inorganic filler, and that the heat curable resin composition is superior in heat resistance and has a high mechanical strength.